Sandra Mitchell, age 11, of Winnipeg, manitoba, Can., for her question:
How does the body use air?
The body cannot survive for more than a few minutes without a constant supply of fresh air. You do not have to use your conscious mind to order the body to breathe day and night. The process goes on automatically, and it is natural to wonder what happens to the constant stream of air which passes into the body and out again.
Air is a filmy nothing, or so it seems. Actually it is a mixture of assorted gases. The vital gas we need is oxygen, and it makes up about 21% of the air we take in with every breath. Oxygen is a very active element, and its atoms are always eager to combine with atoms of other elements to form compounds, Carbon dioxide is a compound made of molecules, each molecule having one atom of carbon and two of oxygen.
Carbon is one of the elements the body takes from food. It finds its way to the living cells of the tissues where it waits far a supply of oxygen. An atom of carbon then combines with two atoms of oxygen to form a molecule of carbon dioxide. This is a chemical process. It gives off heat and energy which the body needs to keep going.
This chemical process is somewhat like a slow burning fire, and the waste product or ashes from the fire is carbon dioxide. It must be removed, for no living thing can exist with its own waste material. The job of delivering the oxygen to the cells and collecting up the waste carbon dioxide is done by the breathing and Circulatory systems working together.
When you breathe ins the air goes down into the moist and spongy lungs. It fills tiny pockets called air sacs. Behind the thin walls of each air sac is a network of fine blood vessels. The blood teems with saucer shaped red cells which contain a chemical called hemoglobin The oxygen atoms in the air sac are attracted through the thin walls and form loose bonds with the hemoglobin. Meantime., the pulsing heart sends the blood stream circulating throughout the body. The cells take the oxygen they need from the blood and give up their waste carbon dioxide. The blood goes back to the lungs and the carbon dioxide seeps into the air sacs. When you breathe out,, you empty the lungs of air and waste carbon dioxide.
The breathing process is carried on by a special center in the brain. It is a group of small cells deep under the nape of the neck., and it works automatically for you day and night. Here the orders which control the breathing process are given without consulting your conscious mind. When you run and use up a lot of energy.. The breathing muscles are ordered to work faster in order to supply the muscles with more oxygen. When you sleep, the breathing muscles are ordered to slow down.